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WWW.HZDR.DE discovered 02.15 TITLE CONTACT _Institute of Resource Ecology at HZDR Dr. Vinzenz Brendler Advantage for calcite That's good news. So it seems highly improbable that dangerous uranyl compounds will make it back to the surface from the depths. Together with colleagues from around the world, HZDR researchers are working to illuminate such reactions and reveal the path taken by the resulting compounds by conducting a wealth of experiments, some of which are carried out in labs deep underground. Analysis specialists identify the substances formed using the latest spectroscopy methods, which involve measuring light beams emitted or influenced by the compounds. The results then end up in enormous databanks that can be accessed by researchers around the world. With these lab experiments, however, HZDR researchers are only able to understand a fraction of the possible reactions between the plethora of compounds that could play a role in and around the planned repository. But that's hardly sufficient to meet demands for the highest level of safety possible. "Without running model simulations on the computer it would be impossible for us to gain a good understanding of this complex system," Vinzenz Brendler assures us. The host of possible reactions threaten to overwhelm even the most high-performance modern computers. Researchers solve this problem by excluding reactions that are obviously unimportant for the end result from their models. In order to come as close as possible to real-life scenarios, they are also taking a look at the cap rock over the salt deposits of Gorleben. "Since this region has been well- researched, we can do some very good model simulations of the area," Vinzenz Brendler explains. "Our computers calculate how and under which environmental conditions radioactive heavy metals and their compounds spread through cap rock and which layers they have a hard time penetrating." It does indeed seem highly unlikely that actinides in the dry salt deposit that has existed for over 200 million years will end up in the cap rock made of clay at all. In order for that to happen, a great deal of water would have to get in. Time and again the computers repeat these selective calculations, but with changes to important factors within their natural limits. So far results show that dramatic fluctuations in the silicate content or the number and electric charge of the ions present will not cause significant changes to the bonding of radioactive substances. Obviously the effect of these two factors is negligible in comparison to others and can therefore be excluded from future model simulations. If, however, the carbonate content or the acid concentration changes then uranium, plutonium, and co. will be contained in the cap rock. "We will therefore be examining these factors in greater detail in the future," Vinzenz Brendler explains. It is just such results that make the HZDR researchers main partners in the German Association for Repository Research (Deutsche Arbeitsgemeinschaft Endlagerforschung) founded at the end of 2013. "Researchers from different organizations have joined the association of their own accord in order to advance research on safe repositories," Vinzenz Brendler summarizes. Funding Vinzenz Brendler's research work is funded by the Federal Ministry of Education and Research (BMBF) as well as other organizations. Among these is THEREDA, an extensive and self-consistent thermodynamic reference databank for the geochemical modeling of solutions and interactions with granite, clay, and salt - which are currently being discussed in Germany as possible host rocks for repositories for highly radioactive waste. The Federal Ministry for Economic Affairs and Energy (BMWi) finances the RES³T databank project, the Rossendorf expert system for surface and sorption thermodynamics, as well as the model work done for the ESTRAL project, which together with the Gesellschaft für Anlagen- und Reaktorsicherheit, GRS (Association for Facility and Reactor Safety) examines the true-to-life integration of sorption processes in transport programs for long-term safety analysis. This work has been carried on by the WEIMAR project starting in 2013 (further development of the "Smart K_d" concept for long- term safety analysis). The European Union is another important funding authority. PUBLICATIONS: H. C. Moog, F. Bok, C. M. Marquardt, V. Brendler: "Disposal of nuclear waste in host rock formations featuring high-saline solutions – Implementation of a thermodynamic reference database (THEREDA)", in Applied Geochemistry 2015 (DOI: 10.1016/j.apgeochem.2014.12.016) B. Drobot, R. Steudtner, J. Raff, G. Geipel, V. Brendler, S. Tsushima: "Combining luminescence spectroscopy, parallel factor analysis and quantum chemistry to reveal metal speciation - A case study of uranyl(VI) hydrolysis", in Chemical Science 2015 (DOI: 10.1039/C4SC02022G)